It is known that a heating device of this kind includes a heater having a heating portion which generates heat by energization; a housing which contains the heating portion and forms a passage for a heating medium between the housing and the heating portion; a energization controlling means for detecting the temperature of the heating medium in the passage and turning on and off the energization of the heater depending on the detected temperature of the heating medium.
Patent Document 1 discloses a protective device for protecting a water heater for electric vehicles. The protective device is provided with a heating protection means including: a temperature determination means for determining whether or not the temperature of the water heater is higher than a designated temperature based on a value detected with a temperature sensor for detecting temperature of the water heater; an off-instruction means for turning off the switch of the water heater when the temperature of the water heater is higher than the designated temperature according to a result determined by the temperature determination means; and an off-holding means for controlling the off-instruction means so as to hold the off-state of the switch when the temperature of the water heater remains higher than the designated temperature.